Under certain conditions, if coherent light strikes an interface between a dielectric (such as air or glass) and a metallic film (such as gold), it is able to excite the conduction electrons near the metal surface to collective density fluctuations, so-called surface plasmons. In surface plasmon resonance spectroscopy (SPR spectroscopy), this effect is used, among other things, for investigating the adsorption and the properties of an analyte located on the metal surface. For this purpose, the intensity of the light reflected by the metal surface is determined as a function of the angle of incidence. The angle of incidence is varied in this case, for example, using a tiltable or rotatable mirror, via which the light is guided onto the metal surface. Based on the excitation of surface plasmons, an intensity minimum sets in at a certain angle of incidence. The associated angle of incidence depends particularly also on the condition of the analyte.
For a portable utilization of plasmonic analysis methods, a miniaturization of the needed mechanical and optical components is required. From European document EP 1 684 063 A1, a portable biochip scanner is known which includes an SPR unit that is present in the form of a rotating disk. Furthermore, from document US 2007/0139653 A1, a method is known in which a micromirror (MEMS) is used for an SPR-based biosensor. To vary the angle of incidence, a goniometer is used in this case, for example.